[POWERPC] Fixup resources on pci_bus for PCIe PHB when no device is connected

On the 85xx/86xx PCIe controllers if there is no device connected to the
PHB we will still allocate a pci_bus for downstream bus of the virtual
P2P bridge. However the resources allocated to the downstream bus are not
correct and so we just mimic the resources from the upstream pci_bus.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>